The present invention provides a process for producing PBI polymer with continuous polymerization with agitation throughout the melt to solid phase change, thus a single-stage process as opposed to the standard two-stage solid-state polymerization “SSP” process. A single-stage process would be beneficial to the commercial process since the current reactors are sized to be large enough to account for the high degree of foam state observed during the first stage of the current reaction process.
Single-stage polymerization of polybenzimidazole has been demonstrated before in U.S. Pat. Nos. 3,509,108 and 4,312,976. Prince's U.S. Pat. No. 3,509,108 claimed a one-stage polymerization process at elevated temperature 460–500° C. and high pressure to 500 psig. Choe's U.S. Pat. No. 4,312,976 claimed a single-stage melt polymerization process with TAB plus IPA (isophthalic, or a dicarboxylic acid) in the presence of a catalyst (up to 1% by wt.) to produce high molecular weight PBI polymer. The monomers are reacted at a temperature higher than their melting temperature, 340–450° C., at atmospheric pressure at least, to produce inherent viscosities of at least 0.5.
The high pressure taught in the Prince reference makes this process costly and difficult to run. Choe's reference eliminates the need for the high pressures taught by Prince but requires the addition of a catalyst. Consequently the commercial product has been made with a two-stage process as taught by Ward U.S. Pat. No. 4,672,104 for the production of polybenzimidazoles.
Inherent viscosity (hereinafter “IV”) is the ratio of the specific viscosity of a solution of known concentration to the concentration of solute extrapolated to zero concentration, measured in units of dL/g. Inherent or intrinsic viscosity is also called the limiting viscosity number. It is directly proportional to the polymer-average molecular weight. dL/g, IV (inherent viscosity) measure, is based on the concentration of the polymer sample tested, g/100 ml or g/deciliter. The polymer is dissolved at the 0.4% (w/v) level in 100 ml of 96.5% (±0.5%) sulfuric acid at 80° C. After filtering, an aliquot is measured for IV using a calibrated Cannon-Fenske capillary viscometer in a 25±0.1 C water bath, the flow time (sec.) of the PBI polymer solution measured vs. the dissolving solvent. IV=1 n (t1/t2)/c, where the natural log of the flow time of the PBI solution (t1) over the flow time of the solvent (t2) is divided by the PBI solution concentration.